The present invention relates measuring Angle-Of-Attack (AOA) or Angle-Of-Sideslip (AOS) for an aircraft, and in particular to the use of mass-airflow-based differential pressure for such measuring.
In aircraft applications, it is difficult to measure Angle-Of-Attack (AOA) or Angle-Of-Sideslip (AOS) accurately at low airspeeds with conventional vane, cone, or differential pressure measurement approaches in common use. The means that are suitable for accurately measuring low airspeed and AOS are not compatible with operating over the large speed range of tactical Vertical Take-Off and Landing (VTOL)/Short Take-Off and Vertical Landing (STOVL) aircraft. Such means also lack the necessary attributes that insure covertness such as a low radar cross-section (RCS). Conventional AOA and AOS sensing approaches lack the sensitivity and dynamic range required to accurately measure AOA or AOS at low airspeeds since they are pressure based. Since dynamic pressure is proportional to velocity squared, these techniques work well at moderate to high airspeeds, but are generally unusable below 50 knots airspeed. Modern VTOL/STOVL aircraft have a need for accurately measuring AOS and AOA at speeds below 50 knots.
A mass-airflow-based differential pressure measurement approach is used to sense Angle-Of-Attack (AOA) or Angle-Of-Sideslip (AOS). Sensing ports on opposing sides of an aircraft fuselage are coupled by an enclosed airflow path incorporating a mass airflow sensor. As the longitudinal axis of the aircraft changes direction with respect to the incident airflow, a differential pressure results from one port to the other. The mass airflow sensor detects a resulting airflow that is a function of the AOA or AOS.
In one embodiment, the ports comprise multiple small orifices that feed a common plenum. A solid state mass airflow sensor is placed in the pneumatic plumbing between the pairs of flush ports, The port""s external orifices are small to minimize the possibility of debris, such as insects, ice or other foreign matter from disabling the port. Even if one of the orifices becomes obstructed, the numerous redundant orifices connected to the plenum continue to allow airflow due to the differential pressure.
In one embodiment for angle of sideslip (AOS) measurement, the flush ports are mounted just in front of a cockpit of an aircraft, laterally displaced in mirrored locations from the centerline of the aircraft. The aircraft comprises a Short Take-Off and Vertical Landing (STOVL) aircraft, however, the invention may be extended to any aircraft.